Factors affecting the temporal stability of semipermanent bilayer coatings in capillary electrophoresis prepared using double-chained surfactants.

Surfactants such as didodecyldimethylammonium bromide (DDAB) adsorb onto fused-silica capillaries to form semipermanent bilayer coatings. However, such coatings must be regenerated between runs to maintain efficiency and reproducibility. In this paper, chemical and physical factors affecting the stability of DDAB coatings are investigated. Chemical factors such as ionic strength and the nature of the buffer anion (e.g., from acetate to phosphate), which decrease the critical micelle concentration of DDAB, improve the coating stability. Increasing buffer pH also increases the coating stability. Finally, reducing the capillary diameter and reducing the volume of buffer flushed through the capillary enhance the coating stability. Using 50 mM acetate, pH 5.0, in a 25-microm-i.d. capillary, cationic proteins were separated with efficiencies of 1.05 million plates/m and a run-to-run migration time reproducibility of 0.6-0.8% RSD for 10 successive runs without regeneration of the DDAB coating between runs.